The present invention relates to a lockable hinge joint having two joint members rotatable about a common axis and, more particularly, to a lockable hinge joint comprising a pair of inner shell halves and a pair of outer shell halves riveted together concentrically by a central hinge bolt. The inner shell and the outer shell are capable of mutually turning around at angles from 0.degree. to 180.degree. and capable of being locked at fixed angles by the engagement of a locking pawl provided on the outer shell body in locking slots located on the peripheral edge of a disc portion of the inner shell body.
Conventionally, some positioning lock joints used for folding ladders employ an inner shell member and an outer shell member which are formed separately as integral bodies. In such types of lock joints, fitting and assembly of the internal positioning components present great inconvenience. Not only is the fitting difficult, but also the mounting of the internal locking mechanism results in a reduction of strength, and it may be necessary to provide reinforcement. This reinforcement also brings about an increase in the cost of production. There are other lock joints of multiple-plate combinations, in which the spaces in the interior of the joint are not sufficient for mounting therein the locking mechanism, and as such, the locking mechanism must necessarily be mounted on the outside of the joint. But when the locking mechanism is located on the outside of the joint, there would certainly be damage because of accidental impacts, and also an unharmonious impression of the outer appearance.
In view of the many drawbacks in the conventional positioning joints for folding ladders, the applicant, based on experience in the manufacture of folding ladders and the manufacture of lock joints for many years, has devised and completed a new and improved positioning joint particularly for folding ladders, and, accordingly, it is the main purpose of the present invention to provide a lockable hinge joint for folding aluminum ladders which can be composed and assembled in a most convenient and fast way.
A further object of the present invention is to provide a structure of a lockable hinge joint for folding aluminum ladders which not only can be manufactured with more ease but is also able to cut production costs.